Pigments stabilized to acid challenge

ABSTRACT

An electrostatically stabilized ink includes a dispersion which is electrostatically stabilized and comprises a pigment. The ink also includes an ionic amphiphile additive which has a charge center having an opposite charge from a charge center of the dispersion.

RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.10/848,440, filed on May 18, 2004, which is hereby incorporated byreference in its entirety.

BACKGROUND

Pigments used in printing inks tend to be attracted to one another inthe ink. If enough pigment particles become associated, the particlestend to fall out of solution. To prevent this, dispersants are added tothe ink containing the pigment particles.

Dispersants generally use one of two methods for preventing the pigmentparticles from agglomerating. One method uses bulky groups attached tothe pigment particle to prevent (or at least hinder) the pigmentparticles from being able to interact in such a way that they cancoagulate. This method may be referred to as the steric hindrancemethod.

Another method which may be used to prevent the pigment particles fromcoagulating is electrostatic stabilization. This method generallyassociates dispersants with the pigment particles, the dispersantshaving a charged group which has the same charge as the otherdispersants. This causes the individual dispersion complexes(pigment+dispersant) to be repelled from each other. Thus, two pigmentparticles each having a negatively charged dispersant associated with itwill be repelled from each other due to the fact that like charges arerepelled from each other.

Dispersants tend to be selected such that they sufficiently interactwith the pigment particle to form a stabilized dispersion complex. Whileuncommon, it is also possible for a pigment particle to have sufficientsteric hindrance to be sterically stabilized or sufficient charge to beelectrostatically stabilized without the use of a dispersant. As usedherein, dispersion will refer to any particle or complex of particlesthat tend to disperse from each other. Reference to a dispersion complexis a reference to the combination of a pigment and a dispersant whichare associated and which complex tends to be dispersed from otherdispersions.

With electrostatically stabilized pigment dispersions, excursions in pHcan lead to their instability. With present pigmented inks, pH decreaseswith accelerated storage testing time, which can amount to 0.5 pH units.The decrease in pH also heralds an increase in ionic strength, which hasan adverse, shrinking effect on the Debye screening length as well asprotonization of the carboxylate groups on the dispersant. Thus, adouble-barreled threat presents itself to a pigment's stability withshifts in pH over time.

Buffers may be employed to stabilize the pH, but, in order to achievethe buffering capacity to withstand pH drift, a high concentration ofbuffer is used which contributes significantly to the total ionicstrength of the solution and thus lowers the Debye screening length aswell.

The teachings herein below extend to those embodiments which fall withinthe scope of the appended claims, regardless of whether they accomplishone or more of the above-mentioned needs, benefits, or preferences.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic illustration of a fluid deposition systemincluding a fluid supply media according to one exemplary embodiment;

FIG. 2 is a top perspective view of a print cartridge including thefluid supply media according to one exemplary embodiment;

FIG. 3 is a graph showing test results of the protection against acidchallenge provided by CTAOMes in an exemplary embodiment;

FIG. 4 is a graph showing test results of the protection against acidchallenge provided by additional cationic amphiphiles according to someexemplary embodiments;

FIG. 5 is a graph showing test results of the protection against acidchallenge provided by HDMeImBr at various concentrations of HDMeImBraccording to an exemplary embodiment; and

FIG. 6 includes chemical structures for various cationic amphiphilestested for protection against acid challenge according to variousexemplary embodiments.

DETAILED DESCRIPTION

In this application, the term solution is being used to refer, unlessstated otherwise, to a solution having two or more types of particleswhere one particle is dissolved in, suspended in, or otherwisemaintained with the other particle. Most applications of a solutionaccording to the disclosed embodiments tend to be liquid solutions.

Dispersants may use negatively charged groups to repel dispersioncomplexes from each other and keep the pigments from coagulating. Oneexample of such a negatively charge group is a carboxylate group. As thepH of the solution becomes more acidic, the carboxylate group tends toattract more free H+ ions from the solution which transforms thecarboxylate group to a carboxylic acid group. These carboxylic acidgroups are less dispersive than the carboxylate groups (they do not havea negative charge like the carboxylate group has), which means that thedispersant is less able to repel dispersion complexes from each otherand less able to keep the pigments from coagulating and falling out ofsolution (referred to as a loss of turbidity).

It has been a general principle that ionic additives having a chargeopposite that of the dispersion would tend to have a similar effect onthe dispersion as having a solution with a more acidic pH. The disclosedembodiments show results that would not be expected given this currentwisdom and which show that the prevailing wisdom is not entirelyaccurate.

Generally, an ionic additive particle having an opposite charge than thedispersion, but which has sufficient hydrophobicity to interact with thedispersion may avoid causing the dispersion to destabilize and therebycause the pigment particles to coagulate and fall out of solution aswould be predicted given the prevailing wisdom. Thus, for negativelycharged dispersants, a positively charged ion having sufficienthydrophobicity to interact with the dispersion may avoid causing thedispersion to coagulate.

When used with negatively charged dispersion complexes, an additionalbenefit can be realized. As mentioned above, negatively chargeddispersion complexes tend to suffer from a loss of ability to stayseparated as the pH becomes more acidic (i.e. at lower pH levels). Acationic additive with sufficient hydrophobicity to interact with thedispersion may tend to increase the ability of the negatively chargeddispersion to resist a loss of stability as the pH becomes more acidic(i.e. may help the dispersion resist acid challengeddestabilization—referred to herein as protecting the dispersion fromacid challenge).

It is generally advantageous to choose a charge center (the atom orportion(s) of the particle carrying the charge of the particle) for theadditive that is most likely to interact with the charge center of thedispersion. As mentioned above, carboxylate groups are one common groupused to electrostatically stabilize a dispersion. Carboxylate groups aregenerally considered to be soft charge centers having a negative charge(also referred to as a soft base). Thus, according to Pearson's hard andsoft acid-base theory, the best counter ion to be included in theadditive would have a soft charge center having a positive charge (alsoreferred to as a soft acid). Some examples of soft acids includeimidizolium ions, quaternary ammonium ions, phosphonium ions, andsulfonium ions. For a brief discussion of Pearson's hard and softacid-base theory and a list of some hard and soft acids and bases, seeInorganic Chemistry: Principles of Structure and Reactivity, FourthEdition at pages 345-354. Reference to a soft acid, soft base, hardacid, or hard base is also a reference to those acids/bases which areborderline between hard and soft. Reference to a truly soft acid, atruly soft base, a truly hard acid, or a truly hard base is a referenceonly to those acids/bases which are clearly soft/hard.

An additive may also be able to associate favorably with the dispersionitself. An additive may have sufficient hydrophobicity to associatefavorably with the dispersion (generally with the pigment). Fordispersions including large hydrophobic regions, this generally meansthat the additive is more attracted to the hydrophobic environment in asolution (generally characterized by the dispersion) than it is to thehydrophilic environment of the solution (generally characterized by thebulk solvent). The additive may even be significantly more attracted tothe hydrophobic environment in a solution than it is to the hydrophilicenvironment of the solution (e.g. having a concentration in thehydrophobic region that is at least about 10 times that in thehydrophilic region). In other embodiments, the additive may have aconcentration in the hydrophilic region that is no more than about 100times that present in the hydrophobic region. For a discussion ofhydrophobic interactions in colloids and surfactants, see PhysicalChemistry of Surfaces, Fifth Edition, by A. W. Adamson.

Ionic amphiphiles may posses both an appropriate charge center andsufficient hydrophobicity to interact with the dispersion. Ionicamphiphiles having a soft charge center (generally a positive chargecenter—a cation) with a longest carbon side chain, extending from thecharge center, with a length of about 9 to about 20 carbon atoms (C9 toC20) is one example of a group of ionic amphiphiles which may possessufficient hydrophobicity to interact with the dispersion. In anotherembodiment, the longest side chain has a length of at least about 10 andno more than about 16 carbon atoms. In some embodiments, the side chainmay include a total of about 9 to 20 carbon atoms. Further, the sidechain may consist essentially of carbon atoms. The organic side chainmay be a straight chain or may be branched. The organic side chain maybe an alkane, an alkene, and/or include some other group. In someembodiments, the charge center does not have more than one organic sidechain comprising more than five (or potentially no more than one tothree) carbon atoms.

According to some embodiments an additive may be added in limitedquantities and still provide a beneficial contribution to the propertiesof the ink. According to one embodiment, the additive may be present inthe ink in an amount no more than 1 or even 0.5 M (moles/Liter).Further, the additive may be present in the ink in an amount no morethan about 10⁻² or 10⁻³ M. According to some embodiments an additive maybe present in the ink in concentrations of at least 10⁻⁵ M, or theadditive may be present in the ink in an amount that is no less thanabout 10⁻⁴ M.

It is a general principle that even stabilized dispersions willinevitably coagulate and fall out of solution. The typical length oftime that a given formulation can maintain the bulk of the dispersion inthe ink is referred to as the shelf life of the ink. The additive may beable to protect the dispersions from acid challenge to impart asufficient shelf life to the ink. Sufficient shelf life is generallydetermined based on an acceptable amount of time it takes from themanufacture of the ink to the sale and use of the ink. In oneembodiment, a sufficient shelf life is generally considered to be on theorder of at least about two years.

In some embodiments, the additive may be a surfactant or act like asurfactant. Surfactants can impart desirable properties to an ink. Onesuch desirable property may include reducing the amount of bleeding—suchas color to color bleeding and/or black to color bleeding. Bleedingoccurs when one pigment extends (bleeds) into an area intended to solelycontain a pigment of a different color. For example, a yellow coloredpigment might bleed into an area intended to only include a blue coloredpigment. This would cause the area to appear green instead of blue. Itis generally desirable to reduce the amount of bleeding that occurs inthe inks so that the resolution of any resulting image can be increased(i.e. pixels of pigments of different colors can be spaced closertogether).

Additives are generally added to the ink to enhance additionalperformance parameters. As one example, an additive may be added toreduce the tendency of the pigment to bleed. For electrostaticallystabilized dispersions, a single additive may be used which can bothprotect the dispersion from acid challenge and can reduce the amount ofbleeding a pigment exhibits. Such an additive may reduce the amount ofother additives (generally surfactants) that would be needed to reducethe tendency of the pigment to bleed. In one embodiment, the onlysurfactants present in the ink that have a notable effect on thetendency of the pigment to bleed consist essentially of additives thatalso protect the dispersion from acid challenge. In a more limitedembodiment, essentially all (e.g. at least 98%) of the surfactants inthe ink that have a significant effect on the tendency of the pigment tobleed also protect the dispersion from acid challenge.

As discussed above, dispersions may become less effective at keeping thepigments in solution as the pH becomes more acidic. To be mosteffective, the ink is initially placed at as high a pH as possible (i.e.as non-acidic as possible). Some inks are intended to be used withprinters that incorporate a silica-based firing chamber/nozzle todispense the ink on a printable medium. If the pH of the ink is toohigh, the ink will tend to attack the silica-based firingchamber/nozzle. An ink intended for use in such a printing applicationgenerally has a pH of no more than about 9 and typically no more thanabout 8.5.

Buffers are generally used at some preset pH, but become less effectiveif the pH is allowed to stray from the preset pH. While most embodimentswill need to balance the considerations listed above to determine thestarting pH of the solution, it would be desirable to use an additivethat is capable of defending against acid challenge as the pH lowersfrom the starting pH. Some embodiments of an additive that protectsagainst acid challenge may be configured to protect against acidchallenge at low pH levels. The ability to protect against acidchallenge may be measured based on the loss of turbidity (the number ofparticles suspended in a volume of solution) of the ink over time at aparticular pH. For instance, in some embodiments, the additive may beable to protect an ink from a substantial loss of turbidity (e.g. nomore than 15% loss) at a pH of 2.23 for a period of at least one hour.In other embodiments, the additive may be able to protect an ink fromessentially all loss of turbidity (e.g. no more than about 3%) at a pHof about 3.0 for a period of at least about 16 hours. Further, theadditive may exhibit an ability to protect against all loss of turbidityunder those conditions during those periods. The additive may be able toachieve any of the results discussed above at a concentration of no morethan about 10⁻² M and potentially at a concentration of no more thanabout 10⁻³ M. This may be referred to as the ability of the additive toresist an acid challenge of a particular pH with a particularconcentration for a particular period of time. For instance, oneembodiment may be able to protect against substantial acid challenge(e.g. no more than a 15% loss of turbidity) of a pH of 3.0 at aconcentration of no more than about 10⁻² M (i.e. of the additive) for atleast about one hour. Another embodiment may be directed to additivesthat can protect against substantial acid challenge at a pH of 6.0 at aconcentration of no more than 0.5 M for at least twelve weeks. Turbiditymay be quantified by measuring (and alternatively referred to as) thelight absorbance of a sample, which absorbance may be measured using aUV-V is spectrophotometer.

When a pigment particle of the ink is not self stabilizing, a commondispersant used to electrostatically stabilize the pigment particle mayinclude a polymer. One type of polymer that may be used is a polyacrylicacid or a copolymer of acrylic acid. Reference to a polymer of acrylicacid could refer to either polyacrylic acid or a copolymer of acrylicacid.

The ink may further include biocides to inhibit growth ofmicroorganisms. Exemplary biocides include Ucarcide™, Proxel™, andNuoCept™. Also, sequestering agents such as EDTA may be included toeliminate deleterious effects of heavy metal impurities. Additionally,buffer solutions may be used to control the pH of the ink, although,according to one embodiment, the ink is substantially free of buffersolutions. Other known additives such as viscosity modifiers and otheracrylic or non-acrylic polymers may be added to improve variousproperties of the ink as desired.

A formulation for an ink according to one embodiment includes adispersion (about 0.5% to 10 wt %), one or more cosolvents (0.01 toabout 50 wt % or about 0.1 to about 15 wt %), one or moresurfactants/amphiphiles (0 to about 40 wt % or about 0.1 to about 10 wt%), one or more high molecular weight colloids (0 to about 3 wt %), oneor more buffers (0.00 to about 0.05 wt %). and water (balance). Suitablecosolvents, surfactants, and high molecular weight colloids can be seenin U.S. Pat. Nos. 6,221,932 and 5,133,803, the entire disclosures ofwhich are hereby incorporated by reference to the extent they areconsistent with the present disclosure.

The additives and dispersions described above may be included in an inkto be used in conjunction with a fluid deposition system that depositsthe ink on a medium to form an image.

FIG. 1 schematically illustrates fluid deposition system 10 configuredto deposit a fluid 12 upon a medium 14. Fluid 12 comprises a liquidmaterial such as ink which creates an image upon medium 14. In otherapplications, fluid 12 may include or carry non-imaging materials,wherein system 10 is utilized to precisely and accurately distribute,proportion and locate materials along medium 14.

Medium 14 comprises a structure upon which fluid 12 is to be deposited.In one embodiment, medium 14 comprises a sheet or roll of a cellulosebased or polymeric based material. In other applications, medium 14 maycomprise other structures which are more three dimensional in shape.Other mediums may include textiles, wood, and plastic.

Fluid deposition system 10 generally includes housing 16, mediatransport 18, support 20, fluid ejection system 22, control circuit 24and fluid supply 26. Control circuit 24 may include various types ofprocessing circuitry, digital and/or analog, and may include amicroprocessor, microcontroller, application-specific integrated circuit(ASIC), or other circuitry configured to perform various input/output,control, analysis, and other functions. Media transport 18 comprises adevice configured to move medium 14 relative to fluid ejection system22. Support 20 comprises one or more structures configured to supportand position fluid ejection system 22 relative to media transport 18. Inone embodiment, support 20 is configured to statically support fluidejection system 22 as media transport 18 moves medium 14. In such anembodiment, commonly referred to as a page-wide-array printer, fluidejection system 22 may substantially span a dimension of medium 14.

In another embodiment, support 22 is configured to move fluid ejectionsystem 22 relative to medium 14. For example, support 20 may include acarriage coupled to fluid ejection system 22 and configured to movesystem 22 along a scan axis across medium 14 as medium 14 is being movedby media transport 18. In particular applications, media transport 18may be omitted wherein support 20 and fluid ejection system 22 areconfigured to deposit fluid upon a majority of the surface of medium 14without requiring movement of medium 14.

Fluid ejection system 22 generally comprises a mechanism configured toeject fluid 12 onto medium 14. In one embodiment, fluid ejection system22 comprises a print head having a plurality of injection openings orink jet nozzles 28 configured to dispense fluid 12 in the form of drops30. In other embodiments, fluid ejection system 22 may include otherdevices configured to selectively eject fluid 12 upon medium 14.

Control circuit 24 generally comprises a processor configured togenerate control signals which direct the operation of media transport18, support 20 and fluid ejection system 22. For purposes of disclosure,the term “processor unit” shall mean a conventionally known or futuredeveloped processing unit that executes sequences of instructionscontained in a memory. Execution of the sequences of instructions causesthe processing unit to perform steps such as generating control signals.The instructions may be loaded in a random access memory (RAM) forexecution by the processing unit from a read only memory (ROM), a massstorage device, or some other persistent storage. In other embodiments,hard wired circuitry may be used in place of or in combination withsoftware instructions to implement the functions described. Controlcircuit 24 is not limited to any specific combination of hardwarecircuitry and software, nor to any particular source for theinstructions executed by the processing unit.

As indicated by arrow 32, control circuit 24 receives data signals fromone or more sources representing the image or deposition pattern offluid 12 to be formed on medium 14. The source of such data may comprisea host system such as a computer or a portable memory reading deviceassociated with system 10. Such data signals may be transmitted tocontrol circuit 24 along infrared, optical, electric or by othercommunication modes. Based upon such data signals, control circuit 24generates control signals that direct the movement of medium 14 bytransport 18, that direct the positioning of fluid ejection system 22 bysupport 20 (in those embodiments in which support moves ejection system22) and that direct the timing at which drops 30 of ink 12 are ejectedby nozzles 28 of ejection system 22.

Fluid supply 26 supplies fluid 12 to fluid ejection system 22. Fluidsupply 26 includes fluid source 36, and reservoir 38. Fluid source 36serves as a source of fluid 12 to reservoir 38. In one particularembodiment, fluid source 36 comprises a receptacle or chamber containingfluid 12 that is configured to be releasably or removably coupled toreservoir 38 such that fluid flows into reservoir 38 from fluid source36. For example, fluid source 36 may include a needle which pierces aseptum provided on reservoir 38, wherein fluid 12 from source 36 flowsinto reservoir 38 through the needle. In another embodiment, fluidsource 36 comprises a distinct chamber containing fluid 12 that ispermanently fixed to reservoir 38 and is configured to supply fluid 12to reservoir 38 upon actuation of a valving mechanism associated withsource 36 or reservoir 38. An example of such an arrangement is found inU.S. Pat. No. 6,679,594 by Robert Sesek and Travis J. Parry entitledImaging Media Cartridge Having a Reserve Chamber, the entire disclosuresof which are hereby incorporated by reference to the extent they areconsistent with the present disclosure.

In yet another embodiment, fluid source 36 comprises a distinct sourceof fluid configured to deliver fluid to reservoir 38 through one or moreconduits, such as tubes using gravitational force, one or more pumpingdevices or other flow actuating mechanisms. In such an application,fluid source 36 may provide either a one-way fluid delivery system inwhich fluid flows from source 36 to reservoir 38 or a recirculatingfluid delivery system in which fluid flows from source 36 to reservoir38 and to fluid ejection system 22 and also flows from fluid ejectionsystem 22 to fluid source 36. In other particular applications, fluidmay alternatively return from fluid ejection system 22 directly toreservoir 38. In still other embodiments, fluid source 36 is omitted,wherein the entire supply of fluid for fluid ejection system 22 isprovided from reservoir 38.

FIG. 2 illustrates ink jet print cartridge 100 which is configured to beused by a fluid deposition system such as system 10 described withrespect to FIG. 1. Print cartridge 100 includes fluid ejection system122 and fluid supply 124. Fluid ejection system 122 comprises a printhead having a plurality of nozzles (not shown) configured to eject inkor other fluid. Fluid ejection system 122 is coupled to fluid supply124.

Fluid supply 124 supplies fluid, such as ink, to fluid ejection system122 and includes reservoir 138. Reservoir 138 generally comprises a bodyhaving an interior 146 configured to contain a fluid to be dispensed byejection system 122 and porous mass 140 with antifoaming agents 142. Inthe particular embodiment shown, reservoir 138 is configured to beremovably coupled to a carriage and to be conveyed by the carriage alonga scan axis across a print medium.

Fill port 150 generally comprises an inlet through closure 144, enablingcartridge 100 to be refilled with fluid. In the particular embodimentillustrated, fill port 150 includes a mechanism configured to seal theopening provided by fill port 150 once filling of cartridge 100 iscompleted or is caused. In one application, the sealing mechanism mayautomatically seal any formed opening such as a valving mechanism or aseptum. In another application, fill port 150 may be configured to bemanually closed when not in use.

The following examples are presented to illustrate the presentembodiments and to assist one of ordinary skill in making and using thesame. The examples are not intended in any way to limit the scope of theclaims.

EXAMPLE 1

A first additive includes Cetyl Trimethylammonium Mesylate (CTAOMes)(N,N,N-trimethyl-N-hexadecylammonium methanesulfonate). The CTAOMesadditive was formed by refluxing hexadecyidimethylamine and methylmethanesulfonate (1:1 mole ratio) in acetonitrile overnight. Aftercooling to room temperature the crude CTAOMes crystals separated fromthe reaction mixture. The CTAOMes crystals were then purified by 3×recrystallization from ethyl acetate and the crystals were allowed todry overnight on a Buchner funnel before characterization.

CTAOMes includes a longest carbon side chain length of C16 extending offof the charge center and includes three additional side chains having amethyl group. CTAOMes has a soft charge center, the center being aquaternary ammonium group.

EXAMPLE 2

A magenta pigment from DIC (HPB3001, lot #T020522) and a Cabot Cyanself-dispersed pigment (IJX-356, cyan) were investigated for the rate ofcoagulation caused by acid challenge. The loss of pigment turbidity, τ,at λ=276 nm was followed using a Cary 5000NIR spectrophotometer equippedwith a Peltier temperature control circuit and stirrer. The stirringrate was kept at 800 rpm and the temperature at 35° C. throughout theinvestigation. To initiate coagulation a 200 μL aliquot of 0.1M HCI wasadded to the cuvette, containing 3 mL of either the DIC or Cabot pigmentdispersion at a concentration of ca. 10¹³ particles L⁻¹. For those runscontaining both additive and HCI a 200 μL aliquot of the additive wasadded to the cuvette containing the pigment and allowed temperatureequilibration for a few minutes prior to the addition of the HCI. Noloss of τ prior to addition of HCI was observed in the presence ofadditive.

Runs were also conducted using the non-ionic amphiphile Tergitol-15-S-7(T15S7). In the presence of T15S7, complete loss of turbidity occurredin less than twenty minutes. T15S7 slowed the coagulation of thepigment, but did not stabilize the pigment dispersions.

FIG. 3 shows the results of acid challenge in the presence and absenceof CTAOMes. With CTAOMes present at 0.029M there was no decrease in τfor over 60 minutes for the DIC and Cabot pigment dispersions with HCIat pH=2.23. In the absence of CTAOMes complete loss of τ occurred inless than 20 minutes. Also, upon standing in the cuvette, no loss of τwas observed for several days. The coagulated pigment in the absence ofCTAOMes was found clinging to the stirring bar, the sides of the cuvetteand mostly in the solution as strands at the end of the runs.

EXAMPLE 3

Similar turbidity tests were run using additional cationic amphiphilesincluding Lauryl Trimethylammonium Bromide (LTABr), MyristalTrimethylammonium Bromide (MTABr), and CTAOMes. As shown in FIG. 4,LTABr, MTABr and CTAOMes all show inhibition of turbidity loss atconcentrations 0.001M MTABr; 0.005M LTABr and 0.0001M CTAOMes,respectively.

LTABr includes a longest carbon side chain length of C12 extending offof the charge center and includes three additional side chains composedof methyl groups (C1) extending from the charge center. LTABr has a softacid charge center, the center being a quaternary ammonium group.

MTABr includes a longest carbon side chain length of C14 extending offof the charge center and includes three additional side chains composedof methyl groups extending from the charge center. MTABr has a soft acidcharge center, the center being a quaternary ammonium group.

EXAMPLE 4

Similar turbidity tests were run using N-hexadecyl-N-methylimidiazo-liumbromide (HDMeImBr) at differing concentrations. As shown in FIG. 5, thecontrol with HCI acid only, showed a Turbidity that decreased and reacha plateau in about 6-8 minutes. The color curves indicate that theaddition of HDMeImBr at concentration of 0.001M and above inhibitturbidity loss, with a significant slowing of turbidity loss for the0.0001M concentration of HDMeImBr.

HDMeImBr includes a longest carbon side chain length of C16 extendingoff of the charge center and comprises an imidizolium group. Theimidizolium group of HDMeImBr is a soft acid charge center.

ILLUSTRATIVE EMBODIMENTS

A number of illustrative embodiments of the present additives, inks madefrom the additives, and applications incorporating such inks arediscussed herein. The embodiments described are intended to provideillustrative examples of the present additives and uses and are notintended to limit the scope of the claimed subject matter.

One embodiment is directed to an electrostatically stabilized ink. Theink includes a dispersion which is electrostatically stabilized andcomprises a pigment; and an additive comprising an ionic amphiphilehaving an opposite charge from the dispersion.

An additional embodiment provides an electrostatically stabilized ink.The ink comprises a dispersion which is electrostatically stabilized andcomprises a pigment; and a cationic amphiphile.

An additional embodiment provides an electrostatically stabilized ink.The ink comprises a dispersion which is electrostatically stabilized andcomprises a pigment; and a cationic amphiphile comprising a soft chargecenter.

An additional embodiment provides an electrostatically stabilized ink.The ink includes a dispersion which is electrostatically stabilized andcomprises a pigment; and a cationic amphiphile comprising a longestcarbon chain length of about C9 to C17.

An additional embodiment provides an electrostatically stabilized ink.The ink comprises an anionic dispersion which is electrostaticallystabilized and comprises a pigment; and a cationic amphiphile thatprotects the dispersion against acid challenge. The cationic amphiphilehas a concentration of no more than about 0.03 M in the ink.

An additional embodiment provides an electrostatically stabilized ink.The ink comprises an anionic dispersion which is electrostaticallystabilized and comprises a pigment; and a cationic amphiphile that hassufficient hydrophobicity to interact with the dispersion.

An additional embodiment provides an electrostatically stabilized ink.The ink comprises an anionic dispersion which is electrostaticallystabilized and comprises a pigment; and a cationic amphiphile thatreduces a tendency of the pigment to bleed when deposited.

An additional embodiment provides an electrostatically stabilized ink.The ink comprises an anionic dispersion which is electrostaticallystabilized and comprises a pigment and a dispersant; and a cationicamphiphile. The dispersant may be a polymer such as a polymer of acrylicacid.

An additional embodiment provides an electrostatically stabilized ink.The ink comprises an anionic dispersion which is electrostaticallystabilized and comprises a pigment. The ink contains less than 0.005 wt.% of a buffer. The ink may contain less than about 0.001% of a buffer.

An additional embodiment provides a fluid supply. The fluid supplyincludes a reservoir. The reservoir contains an electrostaticallystabilized ink such as the ones previously described.

An additional embodiment provides a fluid deposition system. The systemincludes a fluid-dispensing device configured to dispense fluid upon amedium; and a fluid supply. The fluid supply includes a reservoir havingan interior in fluid communication with a fluid-dispensing device. Thereservoir contains an electrostatically stabilized ink such as the onespreviously described.

An additional embodiment provides a machine-printable item. The itemcomprises a medium capable of retaining ink deposited on the medium; andink deposited on the medium in a form of an image. The ink comprises apigment and an ionic amphiphile.

An additional embodiment provides a machine-printable item. The itemcomprises a medium capable of retaining ink deposited on the medium; andink deposited on the medium in a form of an image. The ink comprisescomponents or lacks components in a similar manner to the illustrativeinks discussed above.

An additional embodiment provides a method for forming anelectrostatically stabilized ink. The method comprises adding adispersion to an ink and adding an ionic amphiphile to the ink. Theresulting ink may take the form of one of the illustrative inksdiscussed above. The dispersion may be formed by adding a dispersant toa pigment particle.

An additional embodiment provides a method of using an electrostaticallystabilized ink having a composition similar to those discussed above.The method comprises placing the ink in a fluid reservoir, anddepositing the ink onto a medium. The medium may be capable of retainingat least a pigment of the ink. The medium may be a cellulose-basedmedium. The ink may be deposited on the medium in a manner such that itforms a desired image. For instance, the ink may be deposited by aprinter in a pattern controlled by a control circuit of the printer.

The invention has been described with reference to various specific andillustrative embodiments and techniques. However, it should beunderstood that many variations and modifications may be made whileremaining within the spirit and scope of the invention. For instance,while the exemplary embodiments are discussed with respect to ionicadditives and dispersants, the scope of the claimed subject matter isnot so limited unless stated otherwise in the claims. Thus, a soft acidmay include, for instance, proton donor particles not having a positivecharge.

1. An electrostatically stabilized ink, comprising: (a) a dispersioncomprising a pigment, the dispersion being electrostatically stabilizedand the dispersion comprising a first charge center having a charge; and(b) an additive comprising an ionic amphiphile comprising a secondcharge center with a charge opposite the charge of the first chargecenter, wherein the ionic amphiphile protects the dispersion againstacid challenge without causing the dispersion to destabilize.
 2. The inkof claim 1, wherein the second charge center is positively charged. 3.The ink of claim 2, wherein the ionic amphiphile has sufficienthydrophobicity to interact with the dispersion.
 4. The ink of claim 2,wherein the second charge center is a soft charge center.
 5. The ink ofclaim 4, wherein the ionic amphiphile comprises a longest carbon chainlength of about C9 to C17.
 6. The ink of claim 2, wherein the ionicamphiphile is a surfactant and reduces the tendency of the pigment tobleed.
 7. The ink of claim 2, wherein the ionic amphiphile is able toprotect the dispersant against substantial acid challenge of a pH of 3.0at a concentration of no more than about 10⁻² M for at least about onehour.
 8. The ink of claim 2, further comprising a biocide.
 9. The ink ofclaim 2, wherein the second charge center is selected from a groupconsisting of an imidizolium ion, a quaternary ammonium ion, aphosphonium ion, and a sulfonium ion.
 10. The ink of claim 2, whereinthe ionic amphiphile comprises a longest carbon chain length of aboutC12 to C16.
 11. The ink of claim 2, wherein the ionic amphiphile doesnot comprise more than one carbon side chain having a longest carbonchain length greater than three carbon atoms.
 12. The ink of claim 2,wherein the ionic amphiphile comprises a branched carbon chain.
 13. Theink of claim 2, wherein the ionic amphiphile comprises a straight carbonchain comprising at least about 9 carbon atoms.
 14. The ink of claim 2,wherein a longest carbon side chain of the ionic amphiphile is an alkaneside chain.
 15. The ink of claim 2, wherein the ionic amphiphile has aconcentration of no more than about 0.01 M in the ink.
 16. The ink ofclaim 1, wherein the dispersion comprises a pigment and a dispersant.17. The ink of claim 16, wherein the dispersant comprises a polymer. 18.The ink of claim 1, wherein the ionic amphiphile has sufficienthydrophobicity to interact with the dispersion.
 19. The ink of claim 1,wherein the ionic amphiphile comprises a soft charge center.
 20. The inkof claim 19, wherein the ionic amphiphile comprises a longest carbonchain length of about C9 to C17.
 21. The ink of claim 1, wherein the inkcomprises surfactants that have an effect on a tendency of the pigmentto bleed; the ionic amphiphile is a surfactant; and the surfactantspresent in the ink that have an effect on the tendency of the pigment tobleed consist essentially of the ionic amphiphile.
 22. Anelectrostatically stabilized ink, comprising: a dispersion which iselectrostatically stabilized and comprises a pigment; and a cationicamphiphile comprising a soft charge center, wherein the cationicamphiphile protects the dispersion against acid challenge withoutcausing the dispersion to destabilize.
 23. The ink of claim 22, whereinthe soft charge center is selected from a group consisting of animidizolium ion, a quaternary ammonium ion, a phosphonium ion, and asulfonium ion.
 24. The ink of claim 22, wherein the cationic amphiphilecomprises a longest carbon chain length of about C9 to C17.
 25. The inkof claim 22, wherein the cationic amphiphile is a surfactant and reducesa tendency of the pigment to bleed.
 26. The ink of claim 22, wherein thedispersion comprises a pigment and a dispersant.
 27. The ink of claim26, wherein the dispersant comprises a polymer.
 28. The ink of claim 22,further comprising a humectant.
 29. The ink of claim 22, furthercomprising a biocide.
 30. The ink of claim 22, wherein the cationicamphiphile comprises a longest carbon chain length of about C9 to C17.31. The ink of claim 30, wherein the cationic amphiphile does notcomprise more than one carbon side chain having more than C3.
 32. Theink of claim 30, wherein the longest carbon side chain is an alkane sidechain.
 33. The ink of claim 30, wherein the longest carbon side chain isa straight side chain.
 34. A machine-printable item, comprising: (a) amedium capable of retaining ink deposited on the medium; and (b) anelectrostatically stabilized ink deposited on the medium in a form of animage; said electrostatically stabilized ink comprising: (i) adispersion comprising a pigment, the dispersion being electrostaticallystabilized, and (ii) a cationic amphiphile, wherein the cationicamphiphile protects the dispersion against acid challenge withoutcausing the dispersion to destabilize.
 35. The item of claim 34, whereinthe cationic amphiphile comprises a soft charge center.
 36. The item ofclaim 34, wherein the cationic amphiphile is a surfactant that reduces atendency of the pigment to bleed.
 37. The item of claim 34, wherein themedium is a cellulose-based medium.